The search for new therapeutic agents has been greatly aided in recent years by a better understanding of the structure of enzymes and other biomolecules associated with diseases. One important class of enzymes that has been the subject of extensive study is protein kinases.
Protein kinases constitute a large family of structurally related enzymes that are responsible for the control of a variety of signal transduction processes within the cell. (See, Hardie, G. and Hanks, S. The Protein Kinase Facts Book, I and II, Academic Press, San Diego, Calif.: 1995). Protein kinases are thought to have evolved from a common ancestral gene due to the conservation of their structure and catalytic function. Almost all kinases contain a similar 250-300 amino acid catalytic domain. The kinases may be categorized into families by the substrates they phosphorylate (e.g., protein-tyrosine, protein-serine/threonine, lipids, etc.). Sequence motifs have been identified that generally correspond to each of these kinase families (See, for example, Hanks, S. K., Hunter, T., FASEB J. 1995, 9, 576-596; Knighton et al., Science 1991, 253, 407-414; Hiles et al., Cell 1992, 70, 419-429; Kunz et al., Cell 1993, 73, 585-596; Garcia-Bustos et al., EMBO J. 1994, 13, 2352-2361).
In general, protein kinases mediate intracellular signaling by effecting a phosphoryl transfer from a nucleoside triphosphate to a protein acceptor that is involved in a signaling pathway. These phosphorylation events act as molecular on/off switches that can modulate or regulate the target protein biological function. These phosphorylation events are ultimately triggered in response to a variety of extracellular and other stimuli. Examples of such stimuli include environmental and chemical stress signals (e.g., osmotic shock, heat shock, ultraviolet radiation, bacterial endotoxin, and H2O2), cytokines (e.g., interleukin-1 (IL-1) and tumor necrosis factor α (TNF-α)), and growth factors (e.g., granulocyte macrophage-colony-stimulating factor (GM-CSF), and fibroblast growth factor (FGF)). An extracellular stimulus may affect one or more cellular responses related to cell growth, migration, differentiation, secretion of hormones, activation of transcription factors, muscle contraction, glucose metabolism, control of protein synthesis, and regulation of the cell cycle.
Many diseases are associated with abnormal cellular responses triggered by protein kinase-mediated events as described above. These diseases include, but are not limited to, autoimmune diseases, inflammatory diseases, bone diseases, metabolic diseases, neurological and neurodegenerative diseases, cancer, cardiovascular diseases, allergies and asthma, Alzheimer's disease, and hormone-related diseases. Accordingly, there has been a substantial effort in medicinal chemistry to find protein kinase inhibitors useful as therapeutic agents.
ERK Kinase
ERK2 is a widely distributed protein kinase that achieves maximum activity when both Thr183 and Tyr185 are phosphorylated by the upstream MAP kinase kinase, MEK1 (Anderson et al., 1990, Nature 343, 651; Crews et al., 1992, Science 258, 478). Upon activation, ERK2 phosphorylates many regulatory proteins, including the protein kinases Rsk90 (Bjorbaek et al., 1995, J. Biol. Chem. 270, 18848) and MAPKAP2 (Rouse et al., 1994, Cell 78, 1027), and transcription factors such as ATF2 (Raingeaud et al., 1996, Mol. Cell Biol. 16, 1247), Elk-1 (Raingeaud et al. 1996), c-Fos (Chen et al., 1993 Proc. Natl. Acad. Sci. USA 90, 10952), and c-Myc (Oliver et al., 1995, Proc. Soc. Exp. Biol. Med. 210, 162). ERK2 is also a downstream target of the Ras/Raf dependent pathways (Moodie et al., 1993, Science 260, 1658) and relays the signals from these potentially oncogenic proteins. ERK2 has been shown to play a role in the negative growth control of breast cancer cells (Frey and Mulder, 1997, Cancer Res. 57, 628) and hyperexpression of ERK2 in human breast cancer has been reported (Sivaraman et al., 1997, J Clin. Invest. 99, 1478). Activated ERK2 has also been implicated in the proliferation of endothelin-stimulated airway smooth muscle cells, suggesting a role for this kinase in asthma (Whelchel et al., 1997, Am. J. Respir. Cell Mol. Biol. 16, 589).
Overexpression of receptor tyrosine kinases such as EGFR and ErbB2 (Arteaga CL, 2002, Semin Oncol. 29, 3-9; Eccles SA, 2001, J Mammary Gland Biol Neoplasia 6:393-406; Mendelsohn J & Baselga J, 2000, Oncogene 19, 6550-65), as well as activating mutations in the Ras GTPase proteins (Nottage M & Siu L L, 2002, Curr Pharm Des 8, 2231-42; Adjei A A, 2001, J Natl Cancer Inst 93, 1062-74) or B-Raf mutants (Davies H. et al., 2002, Nature 417, 949-54; Brose et al., 2002, Cancer Res 62, 6997-7000) are major contributors to human cancer. These genetic alterations are correlated with poor clinical prognosis and result in activation of the Raf-1/2/3-MEK1/2-ERK1/2 signal transduction cascade in a broad panel of human tumors. Activated ERK (i.e. ERK1 and/or ERK2) is a central signaling molecule that is associated with the control of proliferation, differentiation, anchorage-independent cell survival, and angiogenesis, contributing to a number of processes that are important for the formation and progression of malignant tumors. These data show that an ERK1/2 inhibitor will exert pleiotropic activity, including proapoptotic, anti-proliferative, anti-metastatic and anti-angiogenic effects, and will offer a therapeutic opportunity against a very broad panel of human tumors.
There is a growing body of evidence that implicates constitutive activation of the ERK MAPK pathway in the oncogenic behavior of select cancers. Activating mutations of Ras are found in ˜30% of all cancers, with some, such as pancreatic (90%) and colon (50%) cancer, harboring particularly high mutation rates. Ras mutations have also been identified in 9-15% of melanomas, but B-Raf somatic missense mutations conferring constitutive activation are more frequent and are found in 60-66% malignant melanomas. Activating mutations of Ras, Raf and MEK are able to oncogenically transform fibroblasts in vitro, and Ras or Raf mutations in conjunction with the loss of a tumor suppressor gene (e.g. p16INK4A) can cause spontaneous tumor development in vivo. Increased ERK activity has been demonstrated in these models and has also been widely reported in appropriate human tumors. In melanoma, high basal ERK activity resulting from either B-Raf or N-Ras mutations or autocrine growth factor activation is well documented and is associated with rapid tumor growth, increased cell survival and resistance to apoptosis. Additionally, ERK activation is considered a major driving force behind the highly metastatic behavior of melanoma associated with increased expression of both extracellular matrix degrading proteases and invasion-promoting integrins as well as the downregulation of E-cadherin adhesion molecules that normally mediate keratinocyte interactions to control melanocyte growth. These data taken together, indicate ERK as a promising therapeutic target for the treatment of melanoma, a currently untreatable disease.
Aurora Kinase
The Aurora family of serine/threonine kinases is essential for cell proliferation [Bischoff, J. R. & Plowman, G. D. (The Aurora/Ipl1p kinase family: regulators of chromosome segregation and cytokinesis) Trends in Cell Biology 9, 454-459 (1999); Giet, R. and Prigent, C. (Aurora/Ipl1p-related kinases, a new oncogenic family of mitotic serine-threonine kinases) Journal of Cell Science 112, 3591-3601 (1999); Nigg, E. A. (Mitotic kinases as regulators of cell division and its checkpoints) Nat. Rev. Mol. Cell Biol. 2, 21-32 (2001); Adams, R. R, Carmena, M., and Earnshaw, W. C. (Chromosomal passengers and the (aurora) ABCs of mitosis) Trends in Cell Biology 11, 49-54 (2001)]. Inhibitors of the Aurora kinase family therefore have the potential to block growth of all tumour types.
Elevated levels of all Aurora family members are observed in a wide variety of tumour cell lines. Aurora kinases are over-expressed in many human tumors and this is reported to be associated with chromosomal instability in mammary tumors (Miyoshi et al 92: 370, 2001).
The three known mammalian family members, Aurora-A (“1”), B (“2”) and C (“3”), are highly homologous proteins responsible for chromosome segregation, mitotic spindle function and cytokinesis. Aurora expression is low or undetectable in resting cells, with expression and activity peaking during the G2 and mitotic phases in cycling cells. In mammalian cells proposed substrates for Aurora include histone H3, a protein involved in chromosome condensation, and CENP-A, myosin II regulatory light chain, protein phosphatase 1, TPX2, all of which are required for cell division.
Since its discovery in 1997 the mammalian Aurora kinase family has been closely linked to tumorigenesis. The most compelling evidence for this is that over-expression of Aurora-A transforms rodent fibroblasts (Bischoff, J. R., et al. A homologue of Drosophila aurora kinase is oncogenic and amplified in human colorectal cancers. EMBO J. 17: 3052, 1998). Cells with elevated levels of this kinase contain multiple centrosomes and multipolar spindles, and rapidly become aneuploid. The oncogenic activity of Aurora kinases is likely to be linked to the generation of such genetic instability. Indeed, a correlation between amplification of the aurora-A locus and chromosomal instability in mammary and gastric tumours has been observed. (Miyoshi, Y., Iwao, K., Egawa, C., and Noguchi, S. Association of centrosomal kinase STK15/BTAK mRNA expression with chromosomal instability in human breast cancers. Int. J. Cancer 92, 370-373 (2001). (Sakakura, C. et al. Tumor-amplified kinase BTAK is amplified and overexpressed in gastric cancers with possible involvement in aneuploid formation. British Journal of Cancer 84: 824 2001).
The Aurora kinases have been reported to be over-expressed in a wide range of human tumours. Elevated expression of Aurora-A has been detected in over 50% of colorectal (Bischoff, J. R., et al. A homologue of Drosophila aurora kinase is oncogenic and amplified in human colorectal cancers. EMBO J. 17: 3052, 1998) (Takahashi, T., et al. Centrosomal kinases, HsAIRk1 and HsAIRK3, are overexpressed in primary colorectal cancers. Jpn. J. Cancer Res. 91: 1007, 2000), ovarian (Gritsko, T. M. et al. Activation and overexpression of centrosome kinase BTAK/Aurora-A in human ovarian cancer. Clinical Cancer Research 9: 1420, 2003), and gastric tumors (Sakakura, C. et al. Tumor-amplified kinase BTAK is amplified and overexpressed in gastric cancers with possible involvement in aneuploid formation. British Journal of Cancer 84: 824, 2001), and in 94% of invasive duct adenocarcinomas of the breast (Tanaka, T., et al. Centrosomal kinase AIK1 is overexpressed in invasive ductal carcinoma of the breast. Cancer Research. 59: 2041, 1999). Furthermore, high levels of Aurora-A have also been reported in renal, cervical, neuroblastoma, melanoma, lymphoma, pancreatic and prostate tumour cell lines. (Bischoff, J. R., et al. A homologue of Drosophila aurora kinase is oncogenic and amplified in human colorectal cancers. EMBO J. 17: 3052, 1998) (Kimura, M., Matsuda, Y., Yoshioka, T., and Okano, Y. Cell cycle-dependent expression and centrosomal localization of a third human Aurora/Ipl1-related protein kinase, AIK3. Journal of Biological Chemistry 274: 7334, 1999)(Zhou et al. Tumour amplifiec kinase STK15/BTAK induces centrosome amplification, aneuploidy and transformation Nature Genetics 20: 189, 1998)(Li et al. Overexpression of oncogenic STK15/BTAK/Aurora-A kinase in human pancreatic cancer Clin Cancer Res. 9(3): 991, 2003).
Amplification/overexpression of Aurora-A is observed in human bladder cancers and amplification of Aurora-A is associated with aneuploidy and aggressive clinical behaviour (Sen S. et al Amplification/overexpression of a mitotic kinase gene in human bladder cancer J Natl Cancer Inst. 94(17):1320, 2002). Moreover, amplification of the aurora-A locus (20q13) correlates with poor prognosis for patients with node-negative breast cancer (Isola, J. J., et al. Genetic aberrations detected by comparative genomic hybridization predict outcome in node-negative breast cancer. American Journal of Pathology 147: 905, 1995). Aurora-B is highly expressed in multiple human tumour cell lines, including leukemic cells (Katayama et al. Human AIM-1: cDNA cloning and reduced expression during endomitosis in megakaryocyte-lineage cells. Gene 244:1-7). Levels of this enzyme increase as a function of Duke's stage in primary colorectal cancers (Katayama, H. et al. Mitotic kinase expression and colorectal cancer progression. Journal of the National Cancer Institute 91: 1160, 1999). Aurora-C, which is normally only found in germ cells, is also over-expressed in a high percentage of primary colorectal cancers and in a variety of tumour cell lines including cervical adenocarinoma and breast carcinoma cells (Kimura, M., Matsuda, Y., Yoshioka, T., and Okano, Y. Cell cycle-dependent expression and centrosomal localization of a third human Aurora/Ipl1-related protein kinase, AIK3. Journal of Biological Chemistry 274: 7334, 1999). (Takahashi, T., et al. Centrosomal kinases, HsAIRk1 and HsAIRK3, are overexpressed in primary colorectal cancers. Jpn. J. Cancer Res. 91: 1007, 2000).
Based on the known function of the Aurora kinases, inhibition of their activity should disrupt mitosis leading to cell cycle arrest. In vivo, an Aurora inhibitor therefore slows tumor growth and induces regression.
Aurora-2 is highly expressed in multiple human tumor cell lines and levels increase as a function of Duke's stage in primary colorectal cancers (Katayama, H. et al. (Mitotic kinase expression and colorectal cancer progression) Journal of the National Cancer Institute 91: 1160, 1999). Aurora-2 plays a role in controlling the accurate segregation of chromosomes during mitosis. Misregulation of the cell cycle can lead to cellular proliferation and other abnormalities. In human colon cancer tissue, the Aurora-2 protein is over expressed (Bischoff et al., EMBO J., 17: 3052, 1998; Schumacher et al., J. Cell Biol., 143: 1635, 1998; Kimura et al., J. Biol. Chem., 272: 13766, 1997). Aurora-2 is over-expressed in the majority of transformed cells. Bischoff et al found high levels of Aurora-2 in 96% of cell lines derived from lung, colon, renal, melanoma and breast tumors (Bischoff, et al EMBO J. 17: 3052, 1998). Two extensive studies show elevated Aurora-2 in 54% and 68% (Bishoff, et al EMBO J. 17: 3052, 1998)(Takahashi, et al Jpn J Cancer Res. 91: 1007, 2000) of colorectal tumours and in 94% of invasive duct adenocarcinomas of the breast (Tanaka, et al 59: 2041, 1999).
Aurora-1 expression is elevated in cell lines derived from tumors of the colon, breast, lung, melanoma, kidney, ovary, pancreas, CNS, gastric tract and leukemias (Tatsuka, et al 58: 4811, 1998).
High levels of Aurora-3 have been detected in several tumour cell lines, although it is restricted to testis in normal tissues (Kimura, et al 274: 7334, 1999). Over-expression of Aurora-3 in a high percentage (c. 50%) of colorectal cancers has also been documented (Takahashi, et al Jpn J Cancer Res. 91, 1007, 2000). In contrast, the Aurora family is expressed at a low level in the majority of normal tissues, the exceptions being tissues with a high proportion of dividing cells such as the thymus and testis (Bischoff, et al EMBO J. 17: 3052, 1998).
For further review of the role Aurora kinases play in proliferative disorders, see Bischoff, J. R. & Plowman, G. D. (The Aurora/Ipl1p kinase family:regulators of chromosome segregation and cytokinesis) Trends in Cell Biology 9, 454-459 (1999); Giet, R. and Prigent, C. (Aurora/Ipl1p-related kinases, a new oncogenic family of mitotic serine-threonine kinases) Journal of Cell Science 112, 3591-3601 (1999); Nigg, E. A. (Mitotic kinases as regulators of cell division and its checkpoints) Nat. Rev. Mol. Cell Biol. 2, 21-32 (2001); Adams, R. R, Carmena, M., and Earnshaw, W. C. (Chromosomal passengers and the (aurora) ABCs of mitosis) Trends in Cell Biology 11, 49-54 (2001); and Dutertre, S., Descamps, S., & Prigent, P. (On the role of aurora-A in centrosome function) Oncogene 21, 6175-6183 (2002).
Glycogen Synthase Kinase
Glycogen synthase kinase-3 (GSK-3) is a serine/threonine protein kinase comprised of α and β isoforms that are each encoded by distinct genes (Coghlan et al., Chemistry & Biology, 7: 793, 2000; Kim and Kimmel, Curr. Opinion Genetics Dev., 10: 508, 2000). GSK-3 has been implicated in various diseases including diabetes, Alzheimer's disease, CNS disorders such as manic depressive disorder and neurodegenerative diseases, and cardiomyocyte hypertrophy (see, e.g., WO 99/65897; WO 00/38675; Kaytor and Orr, Curr. Opin. Neurobiol., 12: 275, 2000; Haq et al., J. Cell Biol., 151: 117, 2000; Eldar-Finkelman, Trends Mol. Med., 8: 126, 2002). These diseases are associated with the abnormal operation of certain cell signaling pathways in which GSK-3 plays a role.
GSK-3 has been found to phosphorylate and modulate the activity of a number of regulatory proteins. These include glycogen synthase, which is the rate-limiting enzyme required for glycogen synthesis, the microtubule-associated protein Tau, the gene transcription factor β-catenin, the translation initiation factor e1F-2B, as well as ATP citrate lyase, axin, heat shock factor-1, c-Jun, c-myc, c-myb, CREB, and CEPBα. These diverse targets implicate GSK-3 in many aspects of cellular metabolism, proliferation, differentiation and development.
In a GSK-3 mediated pathway that is relevant for the treatment of type II diabetes, insulin-induced signaling leads to cellular glucose uptake and glycogen synthesis. GSK-3 is a negative regulator of the insulin-induced signal in this pathway. Normally, the presence of insulin causes inhibition of GSK-3-mediated phosphorylation and deactivation of glycogen synthase. The inhibition of GSK-3 leads to increased glycogen synthesis and glucose uptake (Klein, et al., PNAS, 93: 8455, 1996; Cross et al., Biochem. J., 303: 21, 1994; Cohen, Biochem. Soc. Trans., 21: 555, 1993; and Massillon et al., Biochem J. 299: 123, 1994; Cohen and Frame, Nat. Rev. Mol. Cell. Biol., 2: 769, 2001). However, where the insulin response is impaired in a diabetic patient, glycogen synthesis and glucose uptake fail to increase despite the presence of relatively high blood levels of insulin. This leads to abnormally high blood levels of glucose with acute and chronic effects that may ultimately result in cardiovascular disease, renal failure and blindness. In such patients, the normal insulin-induced inhibition of GSK-3 fails to occur. It has also been reported that GSK-3 is overexpressed in patients with type II diabetes [WO 00/38675]. Therapeutic inhibitors of GSK-3 are therefore useful for treating diabetic patients suffering from an impaired response to insulin.
Apoptosis has been implicated in the pathophysiology of ischemic brain damage (Li, et al., 1997; Choi, et al., 1996; Charriaut-Marlangue, et al., 1998; Grahm and Chen, 2001; Murphy, et al., 1999; Nicotera, et al., 1999). Recent publications indicate that activation of GSK-3β may be involved in apoptotic mechanisms (Kaytor and Orr, 2002; Culbert, et al., 2001). Studies in rat models of ischemic stroke induced by middle cerebral artery occlusion (MCAO) showed increased GSK-3β expression is following ischemia (Wang, et al., Brain Res, 859: 381, 2000; Sasaki, et al., Neurol Res, 23: 588, 2001). Fibroblast growth factor (FGF) reduced ischemic brain injury after permanent middle cerebral artery occlusion (MCO) in rats (Fisher, et al. 1995; Song, et al. 2002). Indeed, the neuroprotective effects of FGF demonstrated in ischemia models in rats may be mediated by a PI-3 kinase/AKT-dependent inactivation of GSK-3β (Hashimoto, et al., 2002). Thus, inhibition of GSK-3β after a cerebral ischemic event may ameliorate ischemic brain damage.
GSK-3 is also implicated in mycardial infarction. See Jonassen et al., Circ Res, 89:1191, 2001 (The reduction in myocardial infarction by insulin administration at reperfusion is mediated via Akt dependent signaling pathway); Matsui, et al., Circulation, 104:330, 2001 (Akt activation preserves cardiac function and prevents cardiomyocyte injury after transient cardiac ischemia in vivo); Miao, et al., J Mol Cell Cardiol, 32:2397, 2000 (Intracoronary, adenovirus-mediated Akt gene delivery in heart reduced gross infarct size following ischemia-reperfusion injury in vivo); and Fujio, et al., Circulation, 101:660, 2000 (Akt signaling inhibits cardiac myocyte apoptosis in vitro and protects against ischemia-reperfusion injury in mouse heart).
GSK-3 activity plays a role in head trauma. See Noshita, et al., Neurobiol Dis, 9:294, 2002 (Upregulation of Akt/PI3-kinase pathway may be crucial for cell survival after traumatic brain injury) and Dietrich, et al., J Neurotrauma, 13:309, 1996 (Posttraumatic administration of bFGF significantly reduced damaged cortical neurons & total contusion volume in a rat model of traumatic brain injury).
GSK-3 is also known to play a role in psychiatric disorders. See Eldar-Finkelman, Trends Mol Med, 8:126, 2002; Li, et al., Bipolar Disord, 4:137, 2002 (LiCl and Valproic acid, anti-psychotic, mood stabilizing drugs, decrease GSK3 activities and increase beta-catenin) and Lijam, et al., Cell, 90:895, 1997 (Dishevelled KO mice showed abnormal social behavior and defective sensorimotor gating. Dishevelled, a cytoplamic protein involved in WNT pathway, inhibits GSK3beta activities).
It has been shown that GSK3 inhibition by lithium and valproic acid induces axonal remodeling and change synaptic connectivity. See Kaytor & Orr, Curr Opin Neurobiol, 12:275, 2002 (Downregulation of GSK3 causes changes in mirotubule-associated proteins: tau, MAP1 & 2) and Hall, et al., Mol Cell Neurosci, 20:257, 2002 (Lithium and valproic acid induces the formation of growth cone-like structures along the axons).
GSK-3 activity is also associated with Alzheimer's disease. This disease is characterized by the presence of the well-known β-amyloid peptide and the formation of intracellular neurofibrillary tangles. The neurofibrillary tangles contain hyperphosphorylated Tau protein, in which Tau is phosphorylated on abnormal sites. GSK-3 has been shown to phosphorylate these abnormal sites in cell and animal models. Furthermore, inhibition of GSK-3 has been shown to prevent hyperphosphorylation of Tau in cells (Lovestone, et al., Curr. Biol., 4:1077, 1994; and Brownlees et al., Neuroreport 8:3251, 1997; Kaytor and Orr, Curr. Opin. Neurobiol., 12:275, 2000). In transgenic mice overexpressing GSK3, significant increased Tau hyperphosphorylation and abnormal morphology of neurons were observed (Lucas, et al., EMBO J, 20:27, 2001). Active GSK3 accumulates in cytoplasm of pretangled neurons, which can lead to neurofibrillary tangles in brains of patients with AD (Pei, et al., J Neuropathol Exp Neurol, 58:1010, 1999). Therefore, inhibition of GSK-3 slows or halts the generation of neurofibrillary tangles and thus treats or reduces the severity of Alzheimer's disease.
Evidence for the role GSK-3 plays in Alzheimer's disease has been shown in vitro. See Aplin, et al, J Neurochem 67:699, 1996; Sun, et al, Neurosci Lett 321:61, 2002 (GSK3b phosphorylates cytoplasmic domain of Amyloid Precursor Protein (APP) and GSK3b inhibition reduces Ab40 & Ab42 secretion in APP-transfected cells); Takashima, et al, PNAS 95:9637, 1998; Kirschenbaum, et al 2001, J Biol Chem 276:7366, 2001 (GSK3b complexes with and phosphorylates presenilin-1, which is associated with gamma-secretase activity in the synthesis of Ab from APP); Takashima, et al, Neurosci Res 31:317, 1998 (Activation of GSK3b by Ab(25-35) enhances phosphorylation of tau in hippocampal neurons. This observation provides a link between Ab and neurofibrillary tangles composed of hyperphosphorylated tau, another pathological hallmark of AD); Takashima, et al, PNAS 90:7789, 1993 (Blockade of GSK3b expression or activity prevents Ab-induced neuro-degeneration of cortical and hippocampal primary cultures); Suhara, et al, Neurobiol Aging. 24:437, 2003 (Intracellular Ab42 is toxic to endothelial cells by interfering with activation of Akt/GSK-3b signaling-dependent mechanism); De Ferrari, et al Mol Psychiatry 8:195, 2003 (Lithium protects N2A cells & primary hippocampal neurons from Ab fibrils-induced cytotoxicity, & reduced nuclear translocation/destabilization of b-catenin); and Pigino, et al., J Neurosci, 23:4499, 2003 (The mutations in Alzheimer's presenilin 1 may deregulate and increase GSK-3 activity, which in turn, impairs axonal transport in neurons. The consequent reductions in axonal transport in affected neurons can ultimately lead to neurodegeneration).
Evidence for the role GSK-3 plays in Alzheimer's disease has been shown in vivo. See Yamaguchi, et al, Acta Neuropathol 92:232, 1996; Pei, et al, J Neuropath Exp Neurol 58:1010, 1999 (GSK3b immunoreactivity is elevated in susceptible regions of AD brains); Hernandez, et al, J Neurochem 83:1529, 2002 (Transgenic mice with conditional GSK3b overexpression exhibit cognitive deficits similar to those in transgenic APP mouse models of AD); De Ferrari, et al Mol Psychiatry 8:195, 2003 (Chronic lithium treatment rescued neurodegeneration and behavioral impairments (Morris water maze) caused by intrahippocampal injection of Ab fibrils.); McLaurin, et al., Nature Med, 8:1263, 2002 (Immunization with Ab in a transgenic model of AD reduces both AD-like neuropathology and the spatial memory impairments); and Phiel, et al Nature 423:435, 2003 (GSK3 regulates amyloid-beta peptide production via direct inhibition of gamma secretase in AD tg mice).
Presenilin-1 and kinesin-1 are also substrates for GSK-3 and relate to another mechanism for the role GSK-3 plays in Alzheimer's disease, as was recently described by Pigino, G., et al., Journal of Neuroscience (23:4499, 2003). It was found that GSK3beta phosphorylates kinsesin-I light chain, which results in a release of kinesin-1 from membrane-bound organelles, leading to a reduction in fast anterograde axonal transport (Morfini et al., 2002). The authors suggest that the mutations in PS1 may deregulate and increase GSK-3 activity, which in turn, impairs axonal transport in neurons. The consequent reductions in axonal transport in affected neurons ultimately lead to neurodegeneration.
GSK-3 is also associated with amyotrophic lateral sclerosis (ALS). See Williamson and Cleveland, 1999 (Axonal transport is retarded in a very early phase of ALS in mSOD1 mice); Morfini et al., 2002 (GSK3 phosphorylates kinesin light chains and inhibit anterograde axonal transport); Warita et al., Apoptosis, 6:345, 2001 (The majority of spinal motor neurons lost the immunoreactivities for both PI3-K and Akt in the early and presymptomatic stage that preceded significant loss of the neurons in this SOD1 tg animal model of ALS); and Sanchez, et al., 2001 (The inhibition of PI-3K induces neurite retraction mediated by GSK3 activation).
GSK-3 activity is also linked to spinal cord and peripheral nerve injuries. It has been shown that GSK3 inhibition by lithium and valproic acid can induce axonal remodeling and change synaptic connectivity. See Kaytor & Orr, Curr Opin Neurobiol, 12:275, 2002 (Downregulation of GSK3 causes changes in mirotubule-associated proteins: tau, MAP1 & 2) and Hall et al., Mol Cell Neurosci, 20:257, 2002 (Lithium and valproic acid induces the formation of growth cone-like structures along the axons). See also Grothe et al., Brain Res, 885:172, 2000 (FGF2 stimulate Schwann cell proliferation and inhibit myelination during axonal growth); Grothe and Nikkhah, 2001 (FGF-2 is up regulated in the proximal and distal nerve stumps within 5 hours after nerve crush); and Sanchez et al., 2001 (The inhibition of PI-3K induces neurite retraction mediated by GSK3 activation).
Another substrate of GSK-3 is β-catenin, which is degraded after phosphorylation by GSK-3. Reduced levels of β-catenin have been reported in schizophrenic patients and have also been associated with other diseases related to increase in neuronal cell death (Zhong et al., Nature, 395:698, 1998; Takashima et al., PNAS, 90:7789, 1993; Pei et al., J. Neuropathol. Exp, 56:70, 1997; and Smith et al., Bioorg. Med. Chem. 11:635, 2001). Furthermore, β-catenin and Tcf-4 play a dual role in vascular remodeling by inhibiting vascular smooth muscle cell apoptosis and promoting proliferation (Wang, et al., Circ Res, 90:340, 2002). Accordingly, GSK-3 is associated with angiogenic disorders. See also Liu, et al., FASEB J, 16:950, 2002 (Activation of GSK3 reduces hepatocyte growth factor, leading to altered endothelial cell barrier function and diminished vascular integrity) and Kim, et al., J Biol Chem, 277:41888, 2002 (GSK3beta activation inhibits angiogenesis in vivo using Matrigel plug assay: the inhibition of GSK3beta signaling enhances capillary formation).
Association between GSK-3 and Huntington's disease has been shown. See Carmichael et al., J Biol Chem., 277:33791, 2002 (GSK3beta inhibition protect cells from poly-glutamine-induced neuronal and non-neuronal cell death via increases in b-catenin and its associated transcriptional pathway). Overexpression of GSK3 reduced the activation of heat shock transcription factor-1 and heat shock protein HSP70 (Bijur et al., J Biol Chem, 275:7583, 2000) that are shown to decrease both poly-(Q) aggregates and cell death in in vitro HD model (Wyttenbach et al., Hum Mol Genet, 11:1137, 2002).
GSK-3 effects the levels of FGF-2 and their receptors are increased during remyelination of brain aggregate cultures remyelinating rat brains. See Copelman et al., 2000, Messersmith, et al., 2000; and Hinks and Franklin, 2000. It was also found that FGF-2 induces process outgrowth by oligodendrocytes implicating involvement of FGF in remyelination (Oh and Yong, 1996; Gogate et al., 1994) and that FGF-2 gene therapy has shown to improve the recovery of experimental allergic encephalomyelitis (EAE) mice (Ruffini, et al., 2001).
GSK-3 has also been associated with hair growth because Wnt/beta-catenin signaling is shown to play a major role in hair follicle morphogenesis and differentiation (Kishimotot et al. Genes Dev, 14:1181, 2000; Millar, J Invest Dermatol, 118:216, 2002). It was found that mice with constitutive overexpression of the inhibitors of Wnt signaling in skin failed to develop hair follicles. Wnt signals are required for the initial development of hair follicles and GSK3 constitutively regulates Wnt pathways by inhibiting beta-catenin. (Andl et al., Dev Cell 2:643, 2002). A transient Wnt signal provides the crucial initial stimulus for the start of a new hair growth cycle, by activating beta-catenin and TCF-regulated gene transcription in epithelial hair follicle precursors (Van Mater et al., Genes Dev, 17:1219, 2003)
Because GSK-3 activity is associated with sperm motility, GSK-3 inhibition is useful as a male contraceptive. It was shown that a decline in sperm GSK3 activity is associated with sperm motility development in bovine and monkey epididymis (Vijayaraghavan et al., Biol Reprod, 54: 709, 1996; Smith et al., J Androl, 20:47, 1999). Furthermore, tyrosine & serine/threonine phosphorylation of GSK3 is high in motile compared to immotile sperm in bulls (Vijayaraghavan et al., Biol Reprod, 62:1647, 2000). This effect was also demonstrated with human sperm (Luconi et al., Human Reprod, 16:1931, 2001).
Src Family Kinases
Another kinase family of particular interest is the Src family of kinases. These kinases are implicated in cancer, immune system dysfunction and bone remodeling diseases. For general reviews, see Thomas and Brugge, Annu. Rev. Cell Dev. Biol. 1997, 13, 513; Lawrence and Niu, Pharmacol. Ther. 1998, 77, 81; Tatosyan and Mizenina, Biochemistry (Moscow) 2000, 65, 49-58; Boschelli et al., Drugs of the Future 2000, 25(7), 717.
Members of the Src family include the following eight kinases in mammals: Src, Fyn, Yes, Fgr, Lyn, Hck, Lck, and Blk. These are nonreceptor protein kinases that range in molecular mass from 52 to 62 kD. All are characterized by a common structural organization that is comprised of six distinct functional domains: Src homology domain 4 (SH4), a unique domain, SH3 domain, SH2 domain, a catalytic domain (SH1), and a C-terminal regulatory region. Tatosyan et al. Biochemistry (Moscow) 2000, 65, 49-58.
Based on published studies, Src kinases are considered as potential therapeutic targets for various human diseases. Mice that are deficient in Src develop osteopetrosis, or bone build-up, because of depressed bone resorption by osteoclasts. This suggests that osteoporosis resulting from abnormally high bone resorption can be treated by inhibiting Src. Soriano et al., Cell 1992, 69, 551 and Soriano et al., Cell 1991, 64, 693.
Suppression of arthritic bone destruction has been achieved by the overexpression of CSK in rheumatoid synoviocytes and osteoclasts. Takayanagi et al., J. Clin. Invest. 1999, 104, 137. CSK, or C-terminal Src kinase, phosphorylates and thereby inhibits Src catalytic activity. This implies that Src inhibition may prevent joint destruction that is characteristic in patients suffering from rheumatoid arthritis. Boschelli et al., Drugs of the Future 2000, 25(7), 717.
Src also plays a role in the replication of hepatitis B virus. The virally encoded transcription factor HBx activates Src in a step required for propagation of the virus. Klein et al., EMBO J. 1999, 18, 5019, and Klein et al., Mol. Cell. Biol. 1997, 17, 6427.
A number of studies have linked Src expression to cancers such as colon, breast, hepatic and pancreatic cancer, certain B-cell leukemias and lymphomas. Talamonti et al., J. Clin. Invest. 1993, 91, 53; Lutz et al., Biochem. Biophys. Res. 1998 243, 503; Rosen et al., J. Biol. Chem. 1986, 261, 13754; Bolen et al., Proc. Natl. Acad. Sci. USA 1987, 84, 2251; Masaki et al., Hepatology 1998, 27, 1257; Biscardi et al., Adv. Cancer Res. 1999, 76, 61; Lynch et al., Leukemia 1993, 7, 1416. Furthermore, antisense Src expressed in ovarian and colon tumor cells has been shown to inhibit tumor growth. Wiener et al., Clin. Cancer Res., 1999, 5, 2164; Staley et al., Cell Growth Diff. 1997, 8, 269.
Other Src family kinases are also potential therapeutic targets. Lck plays a role in T-cell signaling. Mice that lack the Lck gene have a poor ability to develop thymocytes. The function of Lck as a positive activator of T-cell signaling suggests that Lck inhibitors may be useful for treating autoimmune disease such as rheumatoid arthritis. Molina et al., Nature, 1992, 357, 161. Hck, Fgr and Lyn have been identified as important mediators of integrin signaling in myeloid leukocytes. Lowell et al., J. Leukoc. Biol., 1999, 65, 313. Inhibition of these kinase mediators may therefore be useful for treating inflammation. Boschelli et al., Drugs of the Future 2000, 25(7), 717.
JNK Kinase
JNK is a member of the mitogen-activated protein (MAP) kinase family. MAP kinases (MAPKs) are activated by a variety of signals, including growth factors, cytokines, UV radiation, and stress-inducing agents. MAPKs are serine/threonine kinases and their activation occurs by dual phosphorylation of threonine and tyrosine at the Thr-X-Tyr segment in the activation loop. MAPKs phosphorylate various substrates including transcription factors, which in turn regulate the expression of specific sets of genes and thus mediate a specific response to the stimulus.
Three distinct genes, JNK1, JNK2, JNK3 have been identified for this kinase family and at least ten different splicing isoforms of JNKs exist in mammalian cells (Gupta et al., EMBO J. 15:2760, 1996). Members of the JNK family are activated by proinflammatory cytokines, such as tumor necrosis factor-α (TNFα) and interleukin-1 β (IL-1β), as well as by environmental stress, including anisomycin, UV irradiation, hypoxia, and osmotic shock (Minden et al., Biochemica et Biophysica Acta 1333:F85, 1998).
The down-stream substrates of JNKs include transcription factors c-Jun, ATF-2, Elk1, p53, and a cell death domain protein (DENN) (Zhang et al. Proc. Natl. Acad. Sci. USA 1998, 95, 2586-91). Each JNK isoform binds to these substrates with different affinities, suggesting a regulation of signaling pathways by substrate specificity of different JNKs in vivo (Gupta et al., supra).
JNKs, along with other MAPKs, have been implicated in having a role in mediating cellular response to cancer, thrombin-induced platelet aggregation, immunodeficiency disorders, autoimmune diseases, cell death, allergies, osteoporosis and heart disease. The therapeutic targets related to activation of the JNK pathway include chronic myelogenous leukemia (CML), rheumatoid arthritis, asthma, osteoarthritis, ischemia, cancer, and neurodegenerative diseases.
Several reports have detailed the importance of JNK activation associated with liver disease or episodes of hepatic ischemia (Behren, A. et al., Nat. Genet. 1999, 21, 326-9; Onishi, I. et al., FEBS Lett. 1997, 420, 201-4; Parola, M. et al., J. Clin. Invest. 1998, 102, 1942-50; Zwacka, R. M. et al., Hepatology 1998, 28, 1022-30). Therefore, inhibitors of JNK may be useful to treat various hepatic disorders.
A role for JNK in cardiovascular disease such as myocardial infarction or congestive heart failure has also been reported as it has been shown JNK mediates hypertrophic responses to various forms of cardiac stress (Adam, J. W. et al., Circ. Res. 1998, 83, 167-78; Kim, S. et al., Circulation 1998, 97, 1731-7; Liang, F. et al., J. Biol. Chem. 1997, 272, 28050-6; Bogoyevitch, M. A. et al., Circ. Res. 1996, 79, 162-73; Force, T. et al., Circ. Res. 1996, 78, 947-53; Xu, Q. et al., J. Clin. Invest. 1996, 97, 508-14).
It has been demonstrated that the JNK cascade also plays a role in T-cell activation, including activation of the IL-2 promoter. Thus, inhibitors of JNK may have therapeutic value in altering pathologic immune responses (Kempiak, S. et al., J. Immunol. 1999, 162, 3176-87; vanSeventer, G. A. et al., Eur. J. Immunol. 1998, 28, 3867-77; Dubois, B. et al., J. Exp. Med. 1997, 186, 941-53; Wilson, D. J. et al., Eur. J. Immunol. 1996, 26, 989-94).
A role for JNK activation in various cancers has also been established, suggesting the potential use of JNK inhibitors in cancer. For example, constitutively activated JNK is associated with HTLV-1 mediated tumorigenesis (Xu, X. et al., Oncogene 1996, 13, 135-42). JNK may play a role in Kaposi's sarcoma (KS) because it is thought that the proliferative effects of bFGF and OSM on KS cells are mediated by their activation of the JNK signaling pathway (Groopman, J. E. et al., J. Clin. Invest. 1997, 99, 1798-804). Other proliferative effects of other cytokines implicated in KS proliferation, such as vascular endothelial growth factor (VEGF), IL-6 and TNFα, may also be mediated by JNK. In addition, regulation of the c-jun gene in p210 BCR-ABL transformed cells corresponds with activity of JNK, suggesting a role for JNK inhibitors in the treatment for chronic myelogenous leukemia (CML) (Burgess, G. M. et al., Blood 1998, 92, 2450-60).
JNK1 and JNK2 are widely expressed in a variety of tissues. In contrast, JNK3, is selectively expressed in the brain and to a lesser extent in the heart and testis (Gupta et al., supra; Mohit et al., Neuron 1995, 14, 67-78; Martin et al., Brain Res. Mol. Brain Res. 1996, 35, 47-57). JNK3 has been linked to neuronal apoptosis induced by kainic acid, indicating a role of JNK in the pathogenesis of glutamate neurotoxicity. In the adult human brain, JNK3 expression is localized to a subpopulation of pyramidal neurons in the CA1, CA4 and subiculum regions of the hippocampus and layers 3 and 5 of the neocortex (Mohit et al., supra). The CA1 neurons of patients with acute hypoxia showed strong nuclear JNK3-immunoreactivity compared to minimal, diffuse cytoplasmic staining of the hippocampal neurons from brain tissues of normal patients (Zhang et al., supra). Thus, JNK3 appears to be involved involved in hypoxic and ischemic damage of CA1 neurons in the hippocampus.
In addition, JNK3 co-localizes immunochemically with neurons vulnerable in Alzheimer's disease (Mohit et al., supra). Disruption of the JNK3 gene caused resistance of mice to the excitotoxic glutamate receptor agonist kainic acid, including the effects on seizure activity, AP-1 transcriptional activity and apoptosis of hippocampal neurons, indicating that the JNK3 signaling pathway is a critical component in the pathogenesis of glutamate neurotoxicity (Yang et al., Nature 1997, 389, 865-870).
Based on these findings, JNK signalling, especially that of JNK3, has been implicated in the areas of apoptosis-driven neurodegenerative diseases such as Alzheimer's Disease, Parkinson's Disease, ALS (Amyotrophic Lateral Sclerosis), epilepsy and seizures, Huntington's Disease, traumatic brain injuries, as well as ischemic and hemorrhaging stroke.
Accordingly, there is a great need to develop compounds useful as inhibitors of protein kinases. In particular, it would be desirable to develop compounds that are useful as inhibitors of ERK2, JNK3, Src, Aurora2, and GSK3 protein kinases particularly given the inadequate treatments currently available for the majority of the disorders implicated in their activation.